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DESIGN OF REPAIR, RESTORATION AND STRENGTHENING

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• Losses due to any natural hazards are usually significant, but they can become even more significant because of ignorance or lack of willingness to implement an integrated rehabilitation scheme.

• Thus, hasty or erroneous design and /or bad execution of the repairs may lead to increased damage and even loss of human life in future hazards.

• Therefore, there is a need to provide the engineer with all the necessary knowledge for rational design of repair or strengthening, which includes the proper assessment of structural characteristics (including dynamic properties), knowledge of modern techniques and materials for repair and strengthening, design methodology and the appropriate procedure for the execution of the structural rehabilitation.

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Seismic Hazard

• Available seismic resistance : Vc

• Residual seismic resistance: Vd

• If the structure exhibits damage due to the earthquake, Vd is always less than Vc.

• Loss of Seismic resistance: Vc - Vd

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• The engineer must approach the rehabilitation problem of a damaged building in four successive steps.

• 1.Examination of the damaged building• 2.Development of alternate rehabilitation schemes.• 3. Examination of the technical feasibility of

implementing each alternative, a well as its cost estimate and selection of the optimum solution.

• 4. Final rehabilitation solution.• Repair:• The term ‘repair’ means that the damaged structural or

non structural members again reach the minimum strength, stiffness and ductility they ought to have before the hazard. This means that repair is limited only to the damaged elements and in this sense ‘repair’ must be considered as a local intervention.

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Strengthening:

• The term “strengthening” means the increase of the hazard resistance of the structure with interventions beyond repair. This means that in addition to the local interventions to the damaged elements, interventions of global type will be carried out, so that the overall structural behaviour of the building will be improved.

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Strength index:

• In the literature (ATC 3-06, 1978), the strength index is determined as

Rc =Vc/Vb

In practice, for the post earthquake intervention this index is usually is replaced by Rc = Vd/Vc

(Vc-Vd)/Vc[%] Vb

Vb

Vc

Vd repair

strengthening

Seismic resistance V

Fig. schematic presentation of Vb, Vc and Vd.

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Materials and Intervention techniques

1. Conventional cast-n-place concrete2. High strength concrete using shrinkage compensating

admixtures3. Shotcrete (gunite)• Main advantage is absence of forms, very good

adhesion between old and fresh concrete due to high degree of compaction.

4.Polymer concrete: replaces a portion of the conventional cement with certain polymers which are used as certain cementitious modifiers . Vulnerable to fire conditions

5. ResinsEpoxy resins are the most common type used.

6. Resin concrete:7. Grouts.

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Repair and strengthening of structural elements

• Depending on the desirable resistance and the damage level and the type of joints, may be repaired and strengthened with resin injections, replacement of broken off-parts, glued on plates, R/C jackets or metal cages

• The key to the success of the repair or strengthening procedure is to attain a high degree of bonding between the old and the new concrete.

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Repair and strengthening of structural members

Columns.

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Fig.One sided strengthening of a column

1= existing column

2=jacket

3=existing rft.

4= added longitudinal rft.

5= added ties

6=welding

7=bent bars

8=metal plate

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Fig. connection of the old to the new reinforcement of the jacket

(a) Protection of the new bar against buckling with weldings.

(b) Protection of new bars against welding with octogonal ties.

1– Existing column

2 – jacket

3 – Key

4 – bent bars

5 – added reinforcement

6 – ties

7 – welding

8 – alternating corners.

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beams

(a) Local interventions-

resin injection

(b) R/C jackets

rcc jackets.

© Glued metal or FRP sheets.

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Fig. strengthening of a beam on the lower face:

1 – existing rebars

2 – existing stirrups

3 – added longitudinal rebars

4 –added stirrups

5 – welded connecting bar

6 – welding

7 –Collar or angle profiles.

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Fig. Jacket on four sides of a beam:

1 – existing rebars

2 – added longitudinal rebars

3 – added stirrups

4 – welded connecting bar

5 - concrete jacket

6 -- welding

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Welding of a new reinforcement bar

Gluing metal sheets on concrete & Gluing FRP sheets on concrete

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Fig. local repair through the thickness of slab:

a. Repair in the span

b. Repair on the connection of astair to the slab. 1. added rebar, 2. welding,

3. added concrete, 4. existing slab

Fig. Increse in thickness of slab- addition of new rft. a. increase of the thickness on the upper face. b. increase of the thickness of lower face with the addition of new rft. 1. existing slab, 2. added reinforcement, 3. dowel, 4. anchoring bent bars. 5. welded connecting bars.

Fig. Details of connection of a new layer to the old concrete in a slab:

1 existing slab, 2. new slab, 3. sand corner, 4. epoxy glue, 5 epoxied bolts

6. Angle profile, 7. anchor bolts or shoot nails.

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foundations

• Connection of column jacket footing

• Strengthening of footings

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Fig. The end of a column jacket to the footing: 1. new ties, 2. longitudinal rebars, 3 existing concrete, 4. added concrete, 5. dowel in old concrete.

Fig. Anchorage of the column jacket re bar to the footing: 1. old concrete, 2. jacket, 3. longitudinal re bars. 4. new ties, 5. epoxied connections.

Fig. Strengthening of footing – column:

1. Existing foundation, 2. existing column, 3. reinforced jacket, 4. added column, 5. added reinforcement.

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Thank you

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